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3. GQ EMF EF Meter RF Spectrum Power Analyzer

How to measure very short EMF pulse?

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[quote][i]Originally posted by SteveGibson[/i]
[br]GQ People...

I own two EMF-390's (one is a V2) with which I am extremely pleased and impressed. I'm hoping to be able to use it/them to measure the magnetic field strength produced by a very brief (0.4ms) very high-current (40A) pulse through a very low inductance coil (2 layers of 10 turns).

When using the meter, it definitely detects the field at a distance of about 10 inches. But its response with decreasing distance appears to saturate. As we know, the strength of the field created by any dipole -- such as a coil -- changes with the cube of the distance. So, for every halving of the distance we would expect to see an increase in measured field strength of a factor of 8. But this is not what I'm seeing.

This leads me to wonder what assumptions are being made at the sensor end. Should the field be sinusoidal to obtain an expected reading? When the field is being energized, I'm driving the coil's 0.13 ohms with 5 vdc (thus ~40A). But at the end of 0.4ms, I'm open-circuiting the coil to allow it to collapse instantly. So the rate of change of the field is also not symmetrical.

It has occurred to me that I could "characterize" the coil by energizing it with a known low voltage sine wave and use the EMF-390 to measure that field, then calculate the field when scaled up to its operating parameters. But if you guys have any other thoughts about how I might take advantage of your EMF-390v2 for measuring a very short very high gauss field, I'd LOVE to know.

Thanks very much! ... and thanks for the terrific little meter!  :)

[/quote]

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T O P I C R E V I E W
SteveGibson	Posted - 08/29/2020 : 16:44:23 GQ People... I own two EMF-390's (one is a V2) with which I am extremely pleased and impressed. I'm hoping to be able to use it/them to measure the magnetic field strength produced by a very brief (0.4ms) very high-current (40A) pulse through a very low inductance coil (2 layers of 10 turns). When using the meter, it definitely detects the field at a distance of about 10 inches. But its response with decreasing distance appears to saturate. As we know, the strength of the field created by any dipole -- such as a coil -- changes with the cube of the distance. So, for every halving of the distance we would expect to see an increase in measured field strength of a factor of 8. But this is not what I'm seeing. This leads me to wonder what assumptions are being made at the sensor end. Should the field be sinusoidal to obtain an expected reading? When the field is being energized, I'm driving the coil's 0.13 ohms with 5 vdc (thus ~40A). But at the end of 0.4ms, I'm open-circuiting the coil to allow it to collapse instantly. So the rate of change of the field is also not symmetrical. It has occurred to me that I could "characterize" the coil by energizing it with a known low voltage sine wave and use the EMF-390 to measure that field, then calculate the field when scaled up to its operating parameters. But if you guys have any other thoughts about how I might take advantage of your EMF-390v2 for measuring a very short very high gauss field, I'd LOVE to know. Thanks very much! ... and thanks for the terrific little meter! :)
3 L A T E S T R E P L I E S (Newest First)
rfrazier	Posted - 09/03/2020 : 06:51:32 Hi Steve, Good to see you on this forum. This is Ron Frazier, one of your biggest long time fans of the Security Now Podcast and a long time user of Spinrite. I am also a happy GQ EMF-390 owner. I'm not officially associated with GQ other than as a customer. However, I have written extensively on how to use the EMF-390 to it's best abilities as well as the problems associated with taking EMF readings. You may wish to see this post as well as the links it contains. My posts are under the name rfrazier. I also sent you a private email through the GQ Electronics forum system. Good luck with the instrument. How To Sweet Talk You GQ EMF-390 https://www.gqelectronicsllc.com/forum/topic.asp?TOPIC_ID=8856 Sincerely, Ron
SteveGibson	Posted - 08/31/2020 : 17:20:39 quote: Originally posted by EmfDev Hi SteveGibson, the EMF-390 has limitations on the reading. It gets saturated when the EMF is too high. It is really hard to detect a .4ms pulse and if it does it might get saturated. Or unless the software change to increase the sampling rate. Thanks VERY MUCH for your reply. Based upon what I was seeing, this is what I assumed... and I appreciate having some closure. The EMF-390 really is a very nice device! :)
EmfDev	Posted - 08/31/2020 : 09:43:51 Hi SteveGibson, the EMF-390 has limitations on the reading. It gets saturated when the EMF is too high. It is really hard to detect a .4ms pulse and if it does it might get saturated. Or unless the software change to increase the sampling rate.

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